Problem with drivers value's statement
Use a python console



Recommend using a python console or a text editor to crunch in your expressions when they get too complex. See image in the way it has shown the error message.  Most syntax aware text editors have some way to highlight matching brackets, including blender.

Define any variables in your expression first with dummy values

&gt;&gt;&gt; x = 1


Conveniently if using the python console, the math methods are already imported, .

&gt;&gt;&gt; locals().keys()
dict_keys(['__name__', '__doc__', '__package__', '__loader__', '__spec__', '__builtins__', 'bpy', 'C', 'D', 'help', 'Vector', 'Matrix', 'Euler', 'Quaternion', 'Color', 'geometry', 'interpolate', 'noise', 'bvhtree', 'kdtree', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'gcd', 'hypot', 'isclose', 'isfinite', 'isinf', 'isnan', 'ldexp', 'lgamma', 'log', 'log1p', 'log10', 'log2', 'modf', 'pow', 'radians', 'remainder', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'trunc', 'pi', 'e', 'tau', 'inf', 'nan', 'M', 's', 't', 'x', 'bmesh'])


just as most are known to the driver namespace (can be used in driver expressions)

&gt;&gt;&gt; bpy.app.driver_namespace.keys()
dict_keys(['__builtins__', '__name__', '__doc__', '__package__', '__loader__', '__spec__', 'acos', 'acosh', 'asin', 'asinh', 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 'fmod', 'frexp', 'fsum', 'gamma', 'gcd', 'hypot', 'isclose', 'isfinite', 'isinf', 'isnan', 'ldexp', 'lgamma', 'log', 'log1p', 'log10', 'log2', 'modf', 'pow', 'radians', 'remainder', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'trunc', 'pi', 'e', 'tau', 'inf', 'nan', 'bpy', 'noise'])


In the case you crunch in hit enter and the next line presents you with ... it most likely means you are missing a brace.

&gt;&gt;&gt; sqrt(2) * (x - round(x, 0)) if (x % 2) &lt; 1 else sqrt(2) * (x % 2
... 
... )
1.4142135623730951


Test with different input values. The history (up and down arrows) saves retyping everything

&gt;&gt;&gt; x = 0.33
&gt;&gt;&gt; sqrt(2) * (x - round(x, 0)) if (x % 2) &lt; 1 else sqrt(2) * (x % 2)
0.46669047558312143


And when you are happy with it, select it with the mouse  copy CtrlC and then paste CtrlV into the driver expression  

See also defining a driver method and adding to namespace [Find Link]